I can't seem to find the music that's being played in the Dark Chao Garden in Sonic Adventure 2 in any of the official soundtracks.

Here is where the song is being used:

http://www.youtube.com/watch?v=btjVCYgfmdA

It's a part of the Sonic Adventure 2 Unreleased Tracks album in the Galbadia Hotel. Here's a link to it:

http://gh.ffshrine.org/soundtracks/158

Thank you, very much.

You're welcome :)